Liquid impervious, vapor permeable films have become an important article of commerce, finding a wide variety of applications including use as outer covers for personal care products (e.g. diapers or incontinence garments), medical garments, industrial workwear and so forth. By providing an article with high breathability (i.e. high vapor permeability) it is possible to provide a body article that is more comfortable to wear since the migration of water vapor through the fabric helps reduce and/or limit discomfort resulting from excess moisture trapped against the skin. In addition, laminates of such films have found use in various bodily articles as well as numerous other applications. The films can provide the desired barrier properties to the article while other materials laminated thereto can provide additional desired characteristics such as strength, abrasion resistance and/or good hand.
While a variety of breathable films and film laminates are known in the art, one particularly useful laminate uses a breathable barrier comprising a stretched filled microporous film. Such films are typically filled with particles or other matter and then crushed or stretched to form a fine pore network throughout the film. The pores result from the separation of the polymer from the filler. The film pore network allows gas and water vapor to pass through the film while acting as a barrier to liquids and particulate matter. The amount of filler within the film and the degree of stretching is controlled so as to create a network of micropores of a size and/or frequency to impart the desired level of breathability to the fabric. An exemplary stretched filled-film is described in commonly assigned U.S. Pat. No. 5,855,999 to McCormack which discloses a filled-film comprising a predominantly linear polyolefin polymer, a bonding agent and about 30% to 80% by weight calcium carbonate, wherein the filled-film can be stretched to impart the desired degree of porosity to the film. The stretched film may then be laminated to a nonwoven web to create a laminate that takes advantage of the strength and integrity of the nonwoven web and the barrier properties of the stretched film.
While providing a more comfortable personal care product from the wearer's perspective, highly breathable liquid-impervious outer covers often suffer from an unwanted and unpleasant outer cover dampness. Continued use of a personal care article after fluid has been discharged and absorbed by the article can cause the outer cover to develop a wet or damp feel. However, this unpleasant wet feeling is not typically due to permeation of liquid through the liquid-impermeable cover or leakage from the article but is simply condensation on the outer cover resulting from the water vapor passing therethrough. Nevertheless, outer cover dampness is desirably limited to the extent possible.
In addition to breathability of the film and film laminates, the ability of the garment or article to exhibit elastic properties allows the garment to provide better body conformance. However, providing a low cost film or film laminate that achieves the desired conformance and breathability has proven difficult, particularly with microporous filled-films. In order to achieve good body conformance, the polymer composition of the film desirably has good stretch and recovery properties and yet must also be capable of allowing formation and retention of pores within the film. Furthermore, the breathable film laminate must be sufficiently stable so as to maintain the desired characteristics while in use (e.g. at about 37.degree. C. or body temperature) as well as over time and shelf-aging. In this regard, it has been found that such conditions can decrease the breathability and/or reduce the stretch-recovery of the film and/or film laminates.
Thus, there exists a need for films and laminates thereof which are capable of providing good breathability and body conformance. Further, there exists a need for such films and laminates thereof that are sufficiently heat stable to maintain the desired properties when subjected to the conditions commonly experienced in further processing, use, storage and/or transportation. Further, there likewise exists a need for low cost films and film laminates that provide good breathability and body conformance while also providing excellent hand and aesthetic qualities. Still further, there exists a need for absorbent bodily articles which allow sufficient water vapor permeation such that the bodily articles remain comfortable products for the wearer yet which do not allow excessive condensate from water vapor to readily form on the outer cover and create and article having a wet or damp feel.